If the deal -- said to be worth $125 a share for Onyx shareholders -- is completed, Amgen would gain full rights to Kyprolis, a new drug to treat multiple myeloma, Reuters reported. The drug could reach peak sales of more than $2 billion a year, the news agency said, citing analysts.

A spokesman for Amgen told TheStreet.com that his company had no comment. A similar response was received from a spokeswoman for Onyx.